Pulverizer mill



H. R. COLLINS PULVERIZER MILL March 7, 1939.

nFiled Oct. 2l, 1936 Ummm III

Patented Mar. 7, 1939 UNITED S'I'ATE'S yPnLvlmlznnMILL .-Harry R."Cllns,Allentown,'Pa.; "MayI-LCollins administratrx `v of said Harry R.Collins, de-

Application ctober..21, 1936, vSerial No. .106,906

19 Claims.

invention relates -to .pulverizer' .mills especially intended `for the.reduction of non-,me- .tallic vmaterials -such -as coal, limestones andcementaclinker, and in .its more specific aspects .pertains toimprovements rin grinding assemblies thereforiof the typegpreferablycomprisinga plurality ofannular sseries 'of `,grinding elements, such asballs, which cooperate withlgrinding surfaces, at least one of which isrotatably driven in a vhorizontal plane to actuate the balls.

.-Among fthe `objects of the Tpresent :invent-ion may be inoted theprovision of ,an improved grinding'assembly for pulverizing mills, bywhich reduction of the-materialunder treatment is accomplished -in `aplurality of stages, the inven- -tion contemplatingfan arrangement inwhich the grinding assembly of -thestated character-is symmetricallydisposed about .a Vertical axis which constitutes the axis of the driveshaft `for the rotating grinding surface or surfaces of ,the yassembly,lthereby to reduce twisting and/or torsienalstrains to safe limits.Preferablyalso, the grinding vassembly/is arranged asian independentunitbelow the ndriving mechanism for thedrive J shaft, with the-grinding assembly being rcapable of assembly yexteriorly of the millcasing Vfor lowering :thereinto asa unit. There -is `also-provided -aconstruction in which, rupon removal of the driving mechanism, vthe'grinding vassembly vmaybe -readily lifted from the Ymill casing-forreplacement vof .worn parts as is -or may be necessary.

A furtherobject of the .presenti-invention is-the provision yof agrinding assembly in which the weight of certain parts thereof iscarried by a series of the `grinding aelements, thus -to apply grindingpressure thereto, and in which .the :grinding pressures maybeadjusted-to the material under treatment in a ,simple manner and vbyreadily .accessible means, with provision being made'for theregulationof the `degree of neness of the product to -satisfy .varyingrequirements.

lA :further object of theinvention ,is kthe ,provision of -an improvedgrinding .assembly .of ,the

l .stated character, which is self-centering, and in which vprovision ismadeior .compensation of VWearoccurring `on Ythe `grinding halls and/.orthe grinding surfaces with which .the latter v.cooperate, `and which isfurther .so designed that tramp material may pass vthrough the .millwith- `out .injury .tothe grinding-surfaces `or elements. To this endthe rotatable grinding surface or ,surfaces are each resilientlysupported from a rotating part of the grinding assembly .in independentmanner, Mso that vstrains encountered Aby Aonemay be suitably `taken Vupwithout transmis- `sion to ,the other. tAmong the advantages of this.latterarrangement may be .noted enhancediiex- .ibility, .reduced cost,and lesser wear, V,all yby rea- -lson Iof the fact .that ordinary.grinding stresses,

Las well .as stresses occurring .by reason of the `existence of trampparticles in the material being pulverized, Lare 4substantially reducedby reason Aof Athe fact that each .rotary grinding surface `is capable.or substantially .so of A taking .up .through .its vunique .mounting:stresses encountered by it.

Other objects will .be .in part obvious and in part rhereinafter.pointed out inlconnection with the ,accompanying drawings illustratingYin detail certain embodiments of the invention.

VIn these drawings, wherein like Areference .characters designate like.parts throughout ,the several views,-

Eig l is `an elevation, ,partly in section along lines `I-I, `Fig. 2, ofva .pulverizing mill embodyling the improved grinding assembly, certain,parts -being -omitted -for the .sake `of clearness;

Eig. A2 is a partial plan view o'f the grinding assembly;

Fig. V3 is y-a section vgenerally along lines 3-3 of Fig. 2; Y

vFig-fl lis Va broken-away rdetail in section of a :modied construction.y Referring 4to the Adrawings `and more particuvlarly to Figs. 1, 2and-3, reference character Ill rdesignates generally a cylindrical`casing constituted by a lower casing section I.I provided with -a:bottom annular ange l2 which may serve as a .bed plate fortheapparatusgand an upper sec-k -tion -I3. Between the casing sectionsII and I3 i-s arranged'a main bearing-support I4 with bolts 'orequivalent securing means I5 removably se- .curing l:the bearing suportI4 to facing flanges of .the aforesaid casing sections. The upper casingsection I3 is Iprovided. with a horizontal top plate :serving -to closethe top of the casing I.0 as formed by the casing sections aforesaid,and arranged on the .topplate and suitably secured.

' thereto is a vertically disposed motor I6, the

motor shaft (not shown) of .which extends into the l,chamber orcompartment formed by the casing section I3 and the main bearing plateI4. rArranged in said-compartment is a speed reduction mechanism, o'fwhich the vcircular supporting plate .20 vof a ringvgear (not shown) isindicated, the reduction gearing being driven by the motor .shaftaforesaid. The supporting plate 2% of the ring gear issecured as bybolts 22 to a flange 'formed on rthe upper end of a main driving shaft23, the upper portion of which is circular in cross section. Motor i6through speed reduction gearing thus provides a drive for the maindriving shaft 23.

The main bearing plate i4 is provided with a central, elongated hub 25disposed about the circular portion of the shaft 23, there beingprovided suitable bearings between said hub and shaft, provision beingmade for lubricating said bearings, as well as the speed reduction gearas aforesaid. These elements are not shown and described in detail asthey form no part of the present invention except in so far as they mayenter into certain broad combinations hereinafter set forth.

The lower end of the main drive shaft 23 extends downwardly into themill casing section Il and is of square or other angular section. Thesquared lower end of said driving shaft extends through central openingsin upper and lower rotary grinding rings designated 30 land 3|,respectively, and through upper and lower cage rings 32 and 33,respectively, the openings in said grinding and cage rings being of thesame cross section as the lower end of the driving shaft, but beingrslightly larger whereby the shaft may be withdrawn from the rings and topermit the rings free vertical movement as well as some horizontalmovement, thus to maintain alignment and to accommodate for possibleinaccuracies in manufacture or normal wear of the grinding elements. Itwill'be understood that the squared end of the driving shaft 23 providesa driving connection between said shaft and the grinding and cage ringsas aforesaid.

Between the upper and lower grinding rings 33 and 3| is an intermediatefixed ring 35 supported on an inwardly extending shelf or ledge 36formed on the inner wall of the casing section I I. On the upper face ofthe xed ring 35 is arranged a circumferentially channeled raceway 38,suitably secured to the fixed ring, for an upper annular series ofgrinding balls 40, on the upper portions of which engage acircumferentially channeled raceway 4l secured to the under face of therim portion of the upper rotating ring 3B. By this arrangement theweight of the upper ring 3D and of the grinding balls 40 is carried bythe fixed ring 35, with the grinding balls 4D and the grinding surfacesprovided by the raceways 38 and 4I thus forming an upper grinding stage.

On the under face of the xed ring 35 is suitably secured acircumferentially channeled raceway 43 against which engages a lowerannular series of grinding balls 44 carried by a circumferentiallychanneled raceway 45 secured to the upper surface of the rim portion ofthe lower rotating ring 3l. The said grinding balls 44, in conjunctionwith the raceways 43 and 45, constitute the lower grinding stage of thegrinding assembly. Y

Referring now to Fig. 3, upper and lower cage rings 32 and 33 aresecured to each other by a plurality of through bolts 5l), the lowerends of which are preferably headed, the upper ends each being suitablythreaded to receive a spacing nut 5i and a locking nut 52, between whichlatter the upper cage ring 32 is disposed. Said through bolts passthrough suitable apertures 53, 54, provided in the rotating grindingrings 3Q, 3|, respectively, the bolts passing freely through saidapertures and being devoid of connection with said grinding rings. Bythe aforesaid arrangement, cage rings 32, 33 and through bolts 50 form acage which is driven by the shaft 23 to rotate with the grinding rings3U, 3l, the spacing between the cage rings being relatively fixed bysuitable manipulation of the spacing and lock nuts 5|, 52, and the cagebeing positioned vertically by engagement of cage ring 32 with ashoulder 55 formed on driving shaft 23 intermediate its upper circularand lower squared portions, as will be described hereinafter.

Grinding pressure in excess of that afforded by the weight of the uppergrinding ring 30 acting on the grinding balls 40 may be supplemented bya series of compression springs 60 (one being shown in Fig. 1), whichreact between the under face of the cage ring 32 and the top surface ofthe grinding ring 30. The said springs 60 are seated in upwardlyopening, spaced spring pockets 6| in the upper grinding ring 30, theirupper ends bearing against spring heads 62 with which cooperatecompression bolts 64 extending through the top cage ring 32. Byadjusting the bolts 64 to vary the compression of springs 60, grindingpressures may be varied. Lock nuts 63 are provided whereby compressionof springs 60 may be set at a predetermined pressure.

The lower cage ring 33 is disposed below the hub and intermediateportion of the lower grinding ring 3l and is preferably provided with ahorizontal rim portion, between the upper face of which and the undersurface of the lower grinding ring 30 is arranged a plurality ofcompression springs 65 seating in ring pockets 66 and providingV aresilient support-for the lower grinding ring. The compression of thesprings 65 may be adjusted by means of compression bolts 61 andassociated lock nuts 68.

By the above described arrangement, compression springs 60 exert aresilient, downward pressure on the grinding balls 40 of the uppergrinding stage, and compression springs 65 exert an upward grindingpressure on the grinding balls 44 of Vthe lower grinding stage.Preferably, springs 60 and 65 are arranged coaxially and spaceduniformly about the axis of the drive shaft 23 on the same circle onwhich through bolts are arranged, the sets of upper and lower springsalternating with the through bolts, as generally indicated in Fig. 2.While in the construction illustrated four sets of compression springsspaced at an angle of 90 and alternating with through bolts in themanner specified are contemplated, the number of the springs and/orbolts and their relative arrangement may vary in accordance with designrequirements.

It will further be noted that the circumferential channels of theraceways 38, 4l, and 43, 45, have substantially the same curvature asthe grinding balls 40, 44, and that the several grinding surfaces andthe ballsare vertically aligned. Accordingly grinding pressures are atall times exerted in a vertical direction.

In order to direct appropriately the ow of material through the mill,the upper grinding ring 30 is provided with a vertically disposed flange10, to which is bolted or otherwise secured aV circular upwardlyextending dam 1|. Secured to the peripheral edge of the ring 30 is anoutwardly and downwardly inclined bafe 'I2 which terminates short of areversely inclined baffle 13 secured, for example, to the peripheraledge of the lower raceway 33 of the upper grinding stage. Between thebaiiies 12 and 13 is a gap of suitable dimension as to pass material tothe relatively outer side of the grinding balls 4U of the 'charge ofthepulverized material until it has upper stage. The inner peripheral edgeof the lower raceway 38 nof the upper grinding stage may carry aninclined dam 14 over which material reduced in the upper grinding stagepasses and drops downwardly between the inner peripheral edge of the xedring 35 and the intermediate, inclined upper surface of the lowerrotating ring 3 l. Carried on the peripheral edge of the lower ring 3land outwardly of the grinding balls of the lower stage is an adjustableheight dam 15 carrying along its top edge a screen 16.

By the aforesaid arrangement, material spouted into the mill casingVthrough the inlet opening 11 thereof is directed on to the upper rimsurface of the rotating grinding ring 30.

Centrifugal force, due Vto rotation of said ring, thereupon causes suchmaterial to be thrown outwardly whereupon it drops on the baille 12 andis thence directed to the outer side of the grinding balls 40 of theupper stage by the lower baille 13, the flow of material being inwardlythrough the .annular series of grinding balls l. The inner dam 'I4prevents discharge of material from the upper stage until it has beensuitably reduced whereupon material flows over the edge of the dam 14and is directed to the inner side of the grinding balls of the lowergrinding stageythe f flowv of material being outwardly through theannular series of grinding balls 44.

The adjustable heightdam 15- controls disbeen reduced to the desireddegree of neness whereupon the product of final size passes through thescreen 16 and, falling downwardly, is picked up by air entering aforwarding fan (not shown) through air inlet openings 18 formed inthelower casing section I I.

' A grinding assembly as described in the foregoing constitutes aunitary assembly which may be assembled outside of the mill casing on anassembling shaft which is a counterpart of the squared lower end ofdriven shaft 23 and thereupon lowered into the casing as a unit. Theassembly is supportedwithin the casing by the ledge or shelf 36 ooactingwith the fixed grinding ring35, bolts 8B being provided to maintain thexed ring 35 seated on the shelf ring 36;

Upon withdrawal of the driving mechanism, including the main drivingshaft 23, the grinding assembly as aforesaid may be removed as a unitfrom the casing, in which event holding bolts may be -unthreaded andraising bolts 8| may be manipulated to'disturb the seating relationV ofthe fixed ring 35 whereupon the grinding assembly may be lifted from thecasing.

The provision as aforesaid of upper compression springs 60 acting on theupper rotating grinding ring and of lower compression springs 65 actingon the lower rotating grinding ring permits independent adjustment ofthe grinding pressures in the upper and llower stages and at the sametime permits each of the rotating grinding rings to take up stresseswhich it individually encounters without transmitting such stressesrelatively to the other ring. Accordingly, relatively light compressionsprings may be utilized and there results an economy in manufacture anda greater flexibility in use.

In the construction so far described, the cage structure formed by therings`32, 33 and through bolts 50 is rotatably driven with the-grindingrings 3l), 3l, from the drive shaft 23, and while the cage is capable ofvertical movement, it is limited in its upward movement by engagement ofthe upper ring 32 against the drive shaft shoulder 55. The parts are soproportioned and arranged and the strength and compression of springs 60with respect to springs 65 are so selected that in normal operation cagering 32 always bears against shoulder 55, with the result -5 thatsprings 60 and 65 have in effect fixed points of reaction. l

In Fig. 4, wherein is illustrated a modified construction, the lowergrinding ring 3IA is resiliently supported from a spring abutment ring33A which in turn is carried by 4a collar 33B threaded on to thecircular threaded end of the driving shaft 23A, and locked thereto as bycap screws 33C which are preferably wired for safety.

Compression springs 65A react against the abut- 15 ment ring 33A andexert adjustable grinding pressure on the lower grinding balls in themanner described. An upper abutment ring generally'similar to the topcage ring 32, and the upper rotary grinding ring as described in rela-:T240

tion toFigs. 1-3, are provided. However, in the modification described,the through bolts 50 previously described are eliminated, temporaryassembly bolts (not shown) which extend betweenv top and bottom spring.abutment rings being uti- Tg5 lized in their place during assembly andplacement of the grinding assembly in the casing. Upon connection of thecollar 33B to shaft 23A as stated, such temporary holding bolts may bevremoved, and the related sets of upper andlower -f30 lower collar 33B isdisconnected from the drivi235 ing shaft, access being had through thelower end of the casing il); Upon removal of the driving mechanismincluding the driving shaft as aforesaid, the modified grinding assemblymay be bodily lifted from the casing for repair or 9&0

replacement of its parts.

As many changes could be made in carrying out the above constructionswithout departing from the scope of the invention, it is intended .thatall matter contained in the above descripl"45 tion, or shown intheaccompanying drawings, shall be interpreted as illustrative and not in alimiting sense.

I claim:

1. In a pulverizer mill, the combination of up- `5 0 per and lowerrotating grinding rings, an intermediate fixed grinding ring, upper andlower annular series of grinding elements disposed between the upper andintermediate rings and be- .Y tween the intermediate and lower rings,the up-"'55 per and lcwergrinding rings being each provided with acentral shaft opening, a driving shaft extending through saidopeningsand operative to drive the rotating rings, spring means for exertingyielding downward pressure on the grindingq 60 elements of the upperseries, spring means for exerting yielding upward pressure on thegrinding elements of the lower series, each said spring means includinga plurality of springs and a., member against which said springs react,and a65 drive connection between the driving shaft and said members,whereby both said spring means rotate with the rotating grinding rings.

2. In a pulverizer mill, the combination of up? per and lower rotatinggrinding rings, an inter-TO mediate fixed grinding ring, upper and lowerannular series of grinding elements disposed between the upper andintermedaterings and between the intermediate and lower rings, the upperand lower grinding rings being each provided "`7`5 with a central shaftopening, a driving shaft extending through said openings and operativeto drive the rotating rings, spring means for exerting yielding downwardpressure on the grinding elements of the upper series, spring means forexerting yielding upward pressure on the grinding elements of the lowerseries, each said spring means including a plurality of springs, amember against which said springsreact, and means carried by said memberfor adjusting said springs to the desired pressure, and a driveconnection between the drive shaft and said members, wherebyY both saidspring means are rotatable with the rotating grinding rings.

3. In a pulverizer mill, the combination of upper and lower rotatinggrinding rings, an intermediate i'lxed grinding ring, upper and lowerannular series of grinding elements disposed between the upper andintermediate rings and between the intermediate and lower rings, theupper and lower grinding rings'being each provided with a central shaftopening, a spring reacting ring arranged above said upper grinding ring,a spring reacting ring arranged below the lower` grinding ring,independently .operable sets of springs disposed between said springrings and the lupper and lower grinding rings respectively, a drivingshaft extending through the central openings Aof the rotating grindingrings, and means providing a driving connection between the drive shaftand the spring rings.

4. In a pulverizer mill, the combination of upper and lower rotatinggrinding rings, an intermediate xed grinding ring, `upper and lowerannular series of grinding elements disposed between the upper andintermediate rings and between the intermediate and lower rings,`theupper and lower grinding rings being each provided with a central shaftopening, a springreacting ring arranged above said upper grinding ring,a spring reacting ring arranged below the lower grinding ring, saidspring rings each having a central shaft opening, a` driving shaftextending through said openings and operative to drive therotating'grinding rings and the spring rings, and independently operablesets of springs arranged between the spring Vrings and the upper andlower grinding rings respectively.

5. In a pulverizer mill, the combination of upper and lower rotatinggrinding rings, an intermediate ixed grinding ring, upper and lowerannular series of grinding elements disposed between the upper andintermediate rings and between the intermediate and lower rings, theupper and lower grinding rings being each provided with a central shaftopening, a rotating cagestructure supported from the grinding elementsof the upper series inoperative relation to said rotating grindingrings, means carried byksaid cage structure for supporting the lowergrindingY ring and for exerting independent Vyielding pressure on theupper and lower grinding rings, and a driving shaft extending throughthe central openings of the grinding rings and having a drivingconnection with said cage structure.

6. In a pulverizer mill, the combination of upper and lower rotatinggrinding` rings, an intermediate Xed grinding ring, upper and lowerannular series of grinding elements disposed between the upper andintermediate rings and between the intermediate and lower rings, theupper and lower grinding rings being each provided withl a central shaftopening, an upper cage ring operatively related to said upper rotatinggrinding ring, a lower cage ring supported from the upper cagering inoperative relation to the lower rotating grinding ring, the cage ringshaving central shaft openings, a driving shaft extending through thegrinding and cage ring openings, and means operative between the upperand lower cage rings and the upper and lower rotating grinding rings,respectively, for exerting resilient pressure on said rotating grindingrings.

7. In a pulverizer mill, the combination of upper and lower rotatinggrinding rings, an intermediate xed grinding ring, upper and lowerannular series of grinding elements disposed betweenv the upper andintermediate rings and between the intermediate and lower rings, theupper and lower grinding rings being each provided with a central shaftopening, spaced cage rings, the upper of which is operatively related tothe upper rotating grinding ring and the lower is supported from .theupper cage ring in operative relation to the lower rotating grindingring, the

cage rings having central shaft openings, a driving shaft extending,through the grinding and cageV ring openings, and means operativebetween t'he upper and lower cagerrings and the upper and lower rotatinggrinding rings, respec-,l tively, for exerting yielding pressure on thero` tating grinding rings.

8.1In a Vpulverizer mill, Vthe combination of upper and Ylower rotatinggrinding rings, an intermediate fixed grinding ring, upper and lowerannular series of grinding elements disposed between the upper andintermediate rings and Vbetween the intermediate and lower rings, theupper and lower grinding rings being each provided with a central shaftopening, upper and lower cage rings operatively related to the upper andlower rotating grinding rings, respectively, and being each providedwith a central shaft opening, means securing said cage rings in spacedrelation, aplurality of springs operative between the upper cage ringand the upper grinding ring, a plurality of springs operative betweenthe lower cage ring and the lower grinding ring, and a driving shaftextending through the shaft openings of the rotating grinding and cagerings.

,9. In a pulverizer mill, the combination of i upper and lower rotatinggrinding rings, an intermediate fixed grinding ring, upper and lowerannular series of grinding elements disposed between the upper andintermediate rings and between the intermediate and lower rings, theupper Y*and lower grindingV rings being each provided Awith a centralshaft opening, upper and lower cage rings operatively related to theupper and lower rotating grinding rings, respectively, and

being each provided with a central shaft open" ing, Vthrough boltsextending between said cage rings andV operative to space the same, aplurality of springs operative between the upper cage ring and the upperrotating grinding ring, a plurality of springs operative between thelower cage ring and the lower rotating grinding ring, and a drivingshaft extending through the shaft openings of the rotating grinding andcage rings,

whereby the cage rings and the springs are rotatedV with the rotatinggrinding rings.

10. In a pulverizer mill, the combination of upper and lower rotatinggrinding rings, an intermediate fixed grinding ring, upper and lowerannular series of grinding elements disposed between the upper andintermediate rings and between the intermediate and lower rings, theupper and lower grinding rings being each provided with a central shaftopening, an upper cage ring operatively related to the upper grindingring,

amata a` lower cage ring operatively related to.- the. lowergrindingringthe cage rings being each. provided with a central shaftopening, throughbolts extending betweenY said; cage rings` andz throughthe upper and lower grinding rings` forspacing the cage` rings, uppercompression springsA operativeV between. the upper-cage `and grindingvrings, lowerA compression springs operative between thelower grindingand cage rings, and a driving shaft extending through, the shaftopenings of the rotating grinding and cage rings, whereby the cage ringsand the springs are rotated with the rotating grinding rings.

11. In a pulverizer mill, the combination of upper and lower rotatinggrinding rings, an intermediate fixed grinding ring, upper and lowerannular series of grinding elements disposed between the upper andintermediate rings and between the intermediate and lower rings, theupper and lower grinding rings being each provided with a central shaftopening, an upper cage ring operatively related to the upper grindingring, a lower cage ring operatively related to the lower grinding ring,the cage rings being each provided with a central shaft opening, throughbolts eX- tending between said cage rings and through the upper andlower grinding rings for spacing the cage rings, upper compressionsprings operative between the upper cage and grinding rings, lowercompression springs operative between the lower grinding and cage rings,a driving shaft extending through the shaft openings of. the rotatinggrinding and cage rings, whereby the cage rings and the springs arerotated with the rotating grinding rings, and means for adjusting thecompression of the upper and lower springs independently of each other.

12. In a pulverizer mill, the combination of upper and lower rotatinggrinding rings, an intermediate fixed grinding ring, upper and lowerannular series of grinding elements between the upper and intermediaterings and between the intermediate and lower rings, a driving shaft, adriving connection between the shaft and the rotating grinding rings,the upper rotating ring resting on the upper annular series of grindingelements, a suppo-rting ring member effectively disposed below the lowerrotating grinding ring, a driving connection between the driving shaftand the supporting ring member, and means supporting the lower grindingring from the supporting ring member.

13. In a pulverizer mill, the combination of upper and lower rotatinggrinding rings, an intermediate fixed grinding ring, upper and lowerannular series of grinding elements between the upper and intermediaterings and between the intermediate and lower rings, a driving shaft, adriving connection between the shaft and the rotating grinding rings,the upper rotating ring resting on the upper annular series of grindingelements, a supporting ring member effectively disposed below the lowerrotating grinding ring, a driving connection between the driving shaftand the supporting ring member, and means supporting the lower grindingring from the supporting ring member, said means including springs forexerting yielding pressure on the lower grinding ring.

14. In a pulverizer mill, the combination of upper and lower rotatinggrinding rings, an intermediate fixed grinding ring, upper and lowerannular series of grinding elements between the upper and intermediaterings and between the intermediate and lower rings, a driving shaft, a

d riying connection between the shaft andl the rotating grinding rings,the upper rotating ring resting.4 on. theupper annular series ofgrinding elements, a, supporting ring member effectively disposed belowthe lower rotating grinding ring, a driving connection between thedriving shaft and, the supporting ring member, and a pluralit;T of,springs seating on. the supporting ring membei; and operativetherebetween and the lower grinding ring.. y

l5. In a Ypulverizer mill, the combination of upper and lower rotatinggrinding rings, an intermediate fixed grinding ring, upper and lowerannular series of grinding elements between the Lipper and intermediaterings and between the intermediate and lower rings, a driving shaft, adriving connection between the shaft and the rotating grinding rings,the upper rotating ring resting on the upper annular series of grindingelements, means rotating with the upper grinding ring for exertingyielding pressure thereon, a collar carried by the driving shaft androtating therewith, and means yieldingly supporting the lower drivingring from said collar.

16. In a pulverizer mill, the combination of upper and lower rotatinggrinding rings, an intermediate fixed grinding ring, upper and lowerannular series of grinding elements between the upper and intermediaterings and between the intermediate and lower rings, a driving shaft, adriving connection between the shaft and the rotating grinding rings,the upper rotating ring resting on the upper annular series of grindingelements, means rotating with the upper grinding ring for exertingyielding pressure thereon, a supporting collar carried by the drivingshaft and disposed generally below the lower grinding ring, and aplurality of springs carried by the collar and operative between thecollar and the lower grinding ring to exert yielding pressure on thelower grinding ring.

17. In a pulverizer mill, the combination of a casing, a fixed grindingring carried thereby, an upper annular series of grinding elementscarried by the fixed grinding ring, an upper rotating grinding ringcarried by said elements, a rotating ring element arranged above therotating grinding ring driving means, means including said driving meansfor limiting upward movement, of said ring element, means including saidring element for exerting yielding pressure on the upper ring, a lowerrotating grinding ring, a lower annular series of grinding elementscarried thereby and engaging the fixed grinding ring, and means carriedby said driving means for supporting the lower grinding ring.

18. In a pulverizer mill, the combination of a casing, a fixed grindingring carried thereby, an upper annular series of grinding elementscarried by the fixed grinding ring, an upper rotating grinding ringcarried by said elementsa rotating ring element arranged above therotating grinding ring, springs arranged between said ring element andthe upper grinding ring operative to exert yielding pressure on theupper ring, a lower grinding ring, an annular series of rotatinggrinding elements carried thereby and engaging the fixed grinding ring,the upper and lower grinding rings and the ring element being providedwith a shaft opening, a driving shaft extending through said opening,means on the shaft limiting upward movement of the ring element, andmeans carried by said driving shaft for supporting the lower grindingring.

19. In a pulverizer mill, the combination of up- 10 rotating grindingrings, means carried by said cage structure for supporting the lowergrinding ring and for exerting independent yielding pressure on theupper and lower grinding rings, a driving shaft extending through thecentral openings of the rotating grinding rings and having a drivingconnection with said cage structure, and means for positioningvertically the cage structure with reference to the driving shaft.`

HARRY R. COLLINS.

